JavaKit: add CustomJavaClassLoaderConstructible protocol

Swift projections of Java classes can conform to
CustomJavaClassLoaderConstructible, to provide a custom class loader to be used
when constructing new instances.

Fixes: swiftlang#154

Sources/JavaKit/AnyJavaObject.swift

@@ -49,6 +49,19 @@ public protocol AnyJavaObject {
   var javaHolder: JavaObjectHolder { get }
 }
 
+/// Protocol that allows Swift types to specify a custom Java class loader on
+/// initialization. This is useful for platforms (e.g. Android) where the default
+/// class loader does not make all application classes visible.
+public protocol CustomJavaClassLoaderConstructible: AnyJavaObject {
+  static func getJavaClassLoader(in environment: JNIEnvironment) throws -> JavaClassLoader!
+}
+
+/// Add getClassLoader() to JavaObject as it is otherwise recursively defined
+extension JavaObject {
+  @JavaMethod
+  public func getClassLoader() throws -> JavaClassLoader!
+}
+
 extension AnyJavaObject {
   /// Retrieve the underlying Java object.
   public var javaThis: jobject {
@@ -81,13 +94,40 @@ extension AnyJavaObject {
     JavaClass(javaThis: jniClass!, environment: javaEnvironment)
   }
 
-  /// Retrieve the Java class for this type.
-  public static func getJNIClass(in environment: JNIEnvironment) throws -> jclass {
-    try environment.translatingJNIExceptions {
+  /// Retrieve the Java class for this type using the default class loader.
+  private static func _withJNIClassFromDefaultClassLoader<T>(
+    in environment: JNIEnvironment,
+    _ body: (jclass) throws -> T
+  ) throws -> T {
+    let resolvedClass = try environment.translatingJNIExceptions {
       environment.interface.FindClass(
         environment,
         fullJavaClassNameWithSlashes
       )
     }!
+    return try body(resolvedClass)
+  }
+
+  /// Retrieve the Java class for this type using a specific class loader.
+  private static func _withJNIClassFromCustomClassLoader<T>(
+    _ classLoader: JavaClassLoader,
+    in environment: JNIEnvironment,
+    _ body: (jclass) throws -> T
+  ) throws -> T {
+    let resolvedClass = try classLoader.findClass(fullJavaClassName)
+    return try body(resolvedClass!.javaThis)
+  }
+
+  /// Retrieve the Java class for this type and execute body().
+  internal static func withJNIClass<T>(
+    in environment: JNIEnvironment,
+    _ body: (jclass) throws -> T
+  ) throws -> T {
+    if let customConstructible = self as? CustomJavaClassLoaderConstructible.Type,
+       let customClassLoader = try customConstructible.getJavaClassLoader(in: environment) {
+      try _withJNIClassFromCustomClassLoader(customClassLoader, in: environment, body)
+    } else {
+      try _withJNIClassFromDefaultClassLoader(in: environment, body)
+    }
   }
 }

Sources/JavaKit/Exceptions/ExceptionHandling.swift

@@ -39,10 +39,8 @@ extension JNIEnvironment {
     }
 
     // Otherwise, create a exception with a message.
-    _ = interface.ThrowNew(
-      self,
-      try! JavaClass<Exception>.getJNIClass(in: self),
-      String(describing: error)
-    )
+    _ = try! JavaClass<Exception>.withJNIClass(in: self) { exceptionClass in
+      interface.ThrowNew(self, exceptionClass, String(describing: error))
+    }
   }
 }

Sources/JavaKit/Java2Swift.config

@@ -5,6 +5,7 @@
     "java.lang.Byte" : "JavaByte",
     "java.lang.Character" : "JavaCharacter",
     "java.lang.Class" : "JavaClass",
+    "java.lang.ClassLoader" : "JavaClassLoader",
     "java.lang.Double" : "JavaDouble",
     "java.lang.Error" : "JavaError",
     "java.lang.Exception" : "Exception",

Sources/JavaKit/JavaClass+Initialization.swift

@@ -21,9 +21,11 @@ extension JavaClass {
   @_nonoverride
   public convenience init(environment: JNIEnvironment? = nil) throws {
     let environment = try environment ?? JavaVirtualMachine.shared().environment()
-    self.init(
-      javaThis: try ObjectType.getJNIClass(in: environment),
-      environment: environment
-    )
+    var javaClassHolder: JavaObjectHolder!
+
+    javaClassHolder = try ObjectType.withJNIClass(in: environment) { javaClass in
+      JavaObjectHolder(object: javaClass, environment: environment)
+    }
+    self.init(javaThis: javaClassHolder.object!, environment: environment)
   }
 }

Sources/JavaKit/JavaObject+Inheritance.swift

@@ -22,19 +22,17 @@ extension AnyJavaObject {
   private func isInstanceOf<OtherClass: AnyJavaObject>(
     _ otherClass: OtherClass.Type
   ) -> jclass? {
-    guard let otherJavaClass = try? otherClass.getJNIClass(in: javaEnvironment) else {
-      return nil
-    }
+    try? otherClass.withJNIClass(in: javaEnvironment) { otherJavaClass in
+      if javaEnvironment.interface.IsInstanceOf(
+       javaEnvironment,
+       javaThis,
+       otherJavaClass
+     ) == 0 {
+       return nil
+     }
 
-    if javaEnvironment.interface.IsInstanceOf(
-      javaEnvironment,
-      javaThis,
-      otherJavaClass
-    ) == 0 {
-      return nil
+     return otherJavaClass
     }
-
-    return otherJavaClass
   }
 
   /// Determine whether this object is an instance of a specific

Sources/JavaKit/JavaObject+MethodCalls.swift

@@ -253,23 +253,23 @@ extension AnyJavaObject {
     in environment: JNIEnvironment,
     arguments: repeat each Param
   ) throws -> jobject {
-    let thisClass = try Self.getJNIClass(in: environment)
-
-    // Compute the method signature so we can find the right method, then look up the
-    // method within the class.
-    let methodID = try Self.javaMethodLookup(
-      thisClass: thisClass,
-      methodName: javaConstructorName,
-      parameterTypes: repeat (each Param).self,
-      resultType: .void,
-      in: environment
-    )
+    try Self.withJNIClass(in: environment) { thisClass in
+      // Compute the method signature so we can find the right method, then look up the
+      // method within the class.
+      let methodID = try Self.javaMethodLookup(
+        thisClass: thisClass,
+        methodName: javaConstructorName,
+        parameterTypes: repeat (each Param).self,
+        resultType: .void,
+        in: environment
+      )
 
-    // Retrieve the constructor, then map the arguments and call it.
-    let jniArgs = getJValues(repeat each arguments, in: environment)
-    return try environment.translatingJNIExceptions {
-      environment.interface.NewObjectA!(environment, thisClass, methodID, jniArgs)
-    }!
+      // Retrieve the constructor, then map the arguments and call it.
+      let jniArgs = getJValues(repeat each arguments, in: environment)
+      return try environment.translatingJNIExceptions {
+        environment.interface.NewObjectA!(environment, thisClass, methodID, jniArgs)
+      }!
+    }
   }
 
   /// Retrieve the JNI field ID for a field with the given name and type.

Sources/JavaKit/Optional+JavaObject.swift

@@ -70,8 +70,9 @@ extension Optional: JavaValue where Wrapped: AnyJavaObject {
 
   public static func jniNewArray(in environment: JNIEnvironment) -> JNINewArray {
     return { environment, size in
-      let jniClass = try! Wrapped.getJNIClass(in: environment)
-      return environment.interface.NewObjectArray(environment, size, jniClass, nil)
+      try! Wrapped.withJNIClass(in: environment) { jniClass in
+        environment.interface.NewObjectArray(environment, size, jniClass, nil)
+      }
     }
   }
 

Sources/JavaKit/generated/JavaClassLoader.swift

@@ -0,0 +1,72 @@
+// Auto-generated by Java-to-Swift wrapper generator.
+import JavaRuntime
+
+@JavaClass("java.lang.ClassLoader")
+open class JavaClassLoader: JavaObject {
+  @JavaMethod
+  open func getName() -> String
+
+  @JavaMethod
+  open func loadClass(_ arg0: String, _ arg1: Bool) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func loadClass(_ arg0: String) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func setSigners(_ arg0: JavaClass<JavaObject>?, _ arg1: [JavaObject?])
+
+  @JavaMethod
+  open func getClassLoadingLock(_ arg0: String) -> JavaObject!
+
+  @JavaMethod
+  open func findLoadedClass(_ arg0: String) -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func findClass(_ arg0: String) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func findClass(_ arg0: String, _ arg1: String) -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func resolveClass(_ arg0: JavaClass<JavaObject>?)
+
+  @JavaMethod
+  open func defineClass(_ arg0: [Int8], _ arg1: Int32, _ arg2: Int32) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func defineClass(_ arg0: String, _ arg1: [Int8], _ arg2: Int32, _ arg3: Int32) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func findLibrary(_ arg0: String) -> String
+
+  @JavaMethod
+  open func findSystemClass(_ arg0: String) throws -> JavaClass<JavaObject>!
+
+  @JavaMethod
+  open func isRegisteredAsParallelCapable() -> Bool
+
+  @JavaMethod
+  open func getParent() -> JavaClassLoader!
+
+  @JavaMethod
+  open func setDefaultAssertionStatus(_ arg0: Bool)
+
+  @JavaMethod
+  open func setPackageAssertionStatus(_ arg0: String, _ arg1: Bool)
+
+  @JavaMethod
+  open func setClassAssertionStatus(_ arg0: String, _ arg1: Bool)
+
+  @JavaMethod
+  open func clearAssertionStatus()
+}
+extension JavaClass<JavaClassLoader> {
+  @JavaStaticMethod
+  public func getPlatformClassLoader() -> JavaClassLoader!
+
+  @JavaStaticMethod
+  public func getSystemClassLoader() -> JavaClassLoader!
+
+  @JavaStaticMethod
+  public func registerAsParallelCapable() -> Bool
+}

Tests/Java2SwiftTests/Java2SwiftTests.swift

@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import JavaKit
+@testable import JavaKit
 import Java2SwiftLib
 import XCTest // NOTE: Workaround for https://github.com/swiftlang/swift-java/issues/43
 
@@ -661,24 +661,27 @@ func assertTranslatedClass<JavaClassType: AnyJavaObject>(
   translator.translatedClasses[javaType.fullJavaClassName] = (swiftTypeName, nil)
   translator.nestedClasses = nestedClasses
   translator.startNewFile()
-  let translatedDecls = try translator.translateClass(
-    JavaClass<JavaObject>(
-      javaThis: javaType.getJNIClass(in: environment),
-      environment: environment)
-  )
-  let importDecls = translator.getImportDecls()
 
-  let swiftFileText = """
-    // Auto-generated by Java-to-Swift wrapper generator.
-    \(importDecls.map { $0.description }.joined())
-    \(translatedDecls.map { $0.description }.joined(separator: "\n"))
-    """
+  try javaType.withJNIClass(in: environment) { javaClass in
+    let translatedDecls = try translator.translateClass(
+      JavaClass<JavaObject>(
+        javaThis: javaClass,
+        environment: environment)
+    )
+    let importDecls = translator.getImportDecls()
 
-  for expectedChunk in expectedChunks {
-    if swiftFileText.contains(expectedChunk) {
-      continue
-    }
+    let swiftFileText = """
+      // Auto-generated by Java-to-Swift wrapper generator.
+      \(importDecls.map { $0.description }.joined())
+      \(translatedDecls.map { $0.description }.joined(separator: "\n"))
+      """
 
-    XCTFail("Expected chunk '\(expectedChunk)' not found in '\(swiftFileText)'", file: file, line: line)
+    for expectedChunk in expectedChunks {
+      if swiftFileText.contains(expectedChunk) {
+        continue
+      }
+
+      XCTFail("Expected chunk '\(expectedChunk)' not found in '\(swiftFileText)'", file: file, line: line)
+    }
   }
 }